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Astrophotography

A Daytime Occultation of Jupiter

For your location, interpolate between the curves to find the Universal Time of Jupiter’s disappearance and reappearance. South and west of the occultation’s southern limit, the Moon and Jupiter will still make an interesting telescopic pair in the daytime sky.

Sky & Telescope diagram.

The thin waning crescent Moon will occult the second-brightest planet as seen from much of North America on Tuesday, November 9, 2004. The catch is that it will happen in broad daylight, in a bright blue sky (assuming the weather cooperates!). But your telescope still may show this interesting event.

The occultation happens around midday or late morning, with the Moon and Jupiter generally being a little higher than the Sun and fairly far off to its right. Jupiter will disappear behind the Moon’s sunlit limb, with the Moon requiring a minute or more to inch its way across the giant planet’s face. Jupiter will reappear from behind the Moon’s dark edge up to an hour or more later; again the process will be gradual.

To find when these events occur at your location, use the map above (click on the image for a larger version). Interpolate between the lines to find the Universal Time (UT) of each event for your site. (To get Eastern Standard Time, subtract 5 hours from the UT; to get Central Standard Time, subtract 6 hours; to get Mountain, subtract 7.)

The challenge will be finding the Moon and Jupiter at all. Give yourself plenty of time in advance to do this. A lot will depend on the transparency of the sky — in other words, the deepness of its blue color. Point your scope about 38° (nearly four fist-widths at arm’s length) from the Sun, mostly to the right and, for most locations, slightly higher. If you have a polar-aligned equatorial mount, you can be more accurate about it: move about 2 hours 23 minutes west of the Sun, and 15° north of it. (Of course, never risk the chance of accidentally looking at the Sun through a telescope without a solar filter.)

Jupiter’s path behind the Moon as seen from various cities.

Sky & Telescope diagram.

Now sweep around this area looking through your finderscope. Remember that the crescent Moon will have a low surface brightness that will probably make it hardly distinguishable from the sky itself. If you don’t have a good finderscope, use your main telescope’s lowest-power eyepiece. Work slowly and methodically, covering the area in a systematic back-and-forth or spiral pattern, with each sweep overlapping a previous one. If you get too far afield, start over.

Once you’ve got the Moon, the next challenge is Jupiter. Not only will it appear much smaller (a sixtieth of the Moon’s diameter), but worse, it will have an even lower surface brightness. However, the Moon will show you just where to look; the chart above indicates where Jupiter will be located before the occultation as seen from your region.